The invention relates to a colour display tube comprising an envelope consisting of a neck, a cone, and a flat or slightly curved display window having a skirt which is substantially parallel to the axis of the envelope. The inner surface of the display window is joined to the inner surface of the skirt via a sharply curved transition surface. The display window has on its inside a substantially rectangular display screen comprising of a material luminescing in at least one colour and over which an aluminium film is provided. Means is provided in the neck to generate at least one electron beam.
Recently developed display tubes have flatter display windows, such as that described in Journal of Electronic Engineering, August 1982, p. 24. However, even in this tube which has a substantially rectangular display screen the outer contour of the display window is slightly barrel-shaped. For tubes which are placed in a cabinet and have the outer periphery of the display window partly concealed from the viewer by a fillet, this barrel shaped outer contour is not a disadvantage because the inner edge of the fillet can be made to adjoin the edge of the display screen. However, for tubes of the type having a display window which protrudes through the cabinet (so-called "push-through" mounting) where the fillet can not be used, the substantially rectangular display screen on the inner wall of the much less rectangular display window leads to dark areas above and below and on the left and on the right of the displayed picture, which areas vary in width and are annoying to the viewer.